1. Field of the Invention
The invention relates to directly heatable semiconductor bodies useful in diffusion doping processes and somewhat more particularly to directly heatable silicon or silicon carbide tubular bodies and methods of producing such bodies whereby select degrees of conductivity may be provided to select portions of the bodies.
2. Prior Art
Silicon and/or silicon carbide tubes or tubular bodies are especially useful in constructing tubular furnaces or the like, particularly in constructing diffusion furnaces wherein semiconductor components, such as wafers, are positioned within such tubular furnaces and subjected to select diffusion processes. However, silicon and/or silicon carbide tubes can only be heated by direct electrical current flow when the tube ends, which are operationally connected to a voltage source, have a sufficiently low resistance that the heat developed at the tube ends by the passages of current is relatively low while the remaining portion of the tube has sufficient resistivity to allow the desired heating of the tube via direct passage of an applied current.
A method for producing directly heatable silicon and/or silicon carbide tubes is disclosed and claimed by me in U.S. Pat. No. 3,899,557, which is essentially equivalent to German Offenlegungsschrift No. 22 53 411. In the so-disclosed process, two layers of, for example, silicon, are sequentially deposited on the outer surface of the heated carrier member so that the outermost layer of the so-deposited tubular body is doped while the innermost layer is composed of pure silicon. The two layers are pyrolytically deposited from thermally decomposable gaseous silicon compounds, the innermost layer from a silicon compound such as trichlorosilane admixed with hydrogen and the outermost layer from a somewhat similar silicon compound-hydrogen admixture which additionally includes a select amount of a gaseous dopant compound, such as phosphorous trichloride.
Such two layer silicon or silicon carbide tubes are substantially gas-impermeable and are well suited for diffusion processes throughout the entire semiconductor manufacturing sequence. Further, these tubes are extremely attractive for use in diffusion processes since the innermost layer of such tubes has a high degree of purity so that the various semiconductor components placed therein may contact such inner walls without any danger of contamination while the outermost layer of such tubes is sufficiently doped to allow direct passage of an electrical current therethrough so as to heat the overall tube to the desired diffusion temperature.
Nevertheless, a drawback of such two-layered tubes is that the doping thereof must be effected more or less simultaneously with the production process of the tubes and that it is only possible to produce a uniform doping over the entire circumferential surface of the tubes without any possibility of obtaining select doping of select surface areas of the tubes.